Research Analyzes Impact Of Neanderthal Genes On Modern DNA

More than 20 percent of the Neanderthal genome survives in modern human populations, and individuals currently living outside of Africa are composed of between one and four percent Neanderthal DNA, according to a pair of new research papers published on Wednesday.

In the first study, population geneticists Benjamin Vernot and Joshua M. Akey of the University of Washington’s Department of Genome Sciences used a new approach to analyze the whole-genome sequencing data from 665 people from Europe and East Asia. They found over one-fifth of the Neanderthal’s genome lives on in their modern genetic material.

While previous research suggested that someone of non-African descent could have inherited between one and three percent of his or her genome from Neanderthal ancestors, the new study (which appears in the journal Science), used an aggregate of those figures to represent the extent of the Neanderthal genome still present in the study group as a whole.

“The findings are a start to identifying the location of specific pieces of Neanderthal DNA in modern humans and a beginning to creating a collection of Neanderthal lineages surviving in present-day human populations,” according to a statement by Leila Gray of UW Health Sciences/UW Medicine. “To check the accuracy of their approach, Vernot ran their analysis before comparing the suspected Neanderthal sequences they found in modern humans to the recently mapped Neanderthal genome obtained from DNA recovered from bone.”

According to Akey, he and Vernot wanted to ensure how well their predictions matched up with the Neanderthal reference genome, and by doing so, they demonstrated that additional refinement of their methodology could eliminate the need for a reference genome from ancient species to conduct this type of research.

“The results suggest that significant amounts of population-level DNA sequences might be obtained from extinct groups even in the absence of fossilized remains, because these ancient sequences might have been inherited by other individuals from whom scientists can gather genomic data,” Gray said. “Therein lies the potential to discover and characterize previously unknown archaic humans that bred with early humans.”

“It seems quite compelling that as modern humans left Africa, met Neanderthals, and exchanged genes, we picked up adaptive variants in some genes that conferred an advantage in local climatic conditions,” Akey told Ed Yong of National Geographic.

The lack of Neanderthal DNA in other portions of modern non-African DNA suggests their version of the genes were most likely weeded out by natural selection due to the adverse effect they would have had in modern men and women, Yong added.

Likewise, the authors of the second study, which appeared in Wednesday’s edition of the journal Nature, noted that Neanderthal DNA in modern humans have been associated with genes affecting type 2 diabetes, Crohn’s disease, lupus, and smoking habits, as well as the genes responsible for making keratin, the protein found in our skin and hair.

“Now that we can estimate the probability that a particular genetic variant arose from Neanderthals, we can begin to understand how that inherited DNA affects us,” explained senior author David Reich, a genetics professor from Harvard Medical School. “We may also learn more about what Neanderthals themselves were like.”

“The goal was to understand the biological impact of the gene flow between Neanderthals and modern humans. We reasoned that when these two groups met and mixed, some new traits would have been selected for and remained in the human genome, while some incompatibilities would have been selected against and removed,” he added. “This suggests that as humans were adapting to the non-African environment they were moving into, they may have been able to exploit adaptations that Neanderthals had already achieved.”

Reich’s team found that, on average, humans from East Asia have a greater percent of their genome originating from Neanderthals than Europeans. They also found that some genes had variants of Neanderthal origin in over 60 percent of Europeans or Asians, while other genes were never of Neanderthal heritage.

The researchers found the genetic changes most often inherited from Neanderthals pertained primarily to keratin. However, Reich and his colleagues report additional research will be required to determine the exact biological implications of the Neanderthal keratin genes, as well as how they differ from other versions of keratin-related proteins that already existed in modern men and women.